The USB on-the-go (OTG) supplement to the USB specification 2.0 (revision 1.0, published Dec. 18, 2001 and hereby incorporated by reference in its entirety) has been developed to provide a framework for the inclusion of limited USB host capability in devices that were previously simply PC peripherals. Many of the USB products available will soon feature USB OTG rather than basic (legacy) USB capability. As vendors of such products seek to bring the first USB OTG devices to market, architectures that minimize the changes required to existing product designs are desirable. Such configurations allow new products to get to market as quickly as possible with as little additional investment as possible.
The installed base of USB peripherals is in the hundreds of millions of devices, and is continuing to grow rapidly. Although many USB devices are simple input devices (i.e., mice, keyboards, etc.), many of the highest volume USB devices are products such as mass storage devices (i.e., hard disks, flash cards, CD-ROM drives, etc.), MP3 players, digital still cameras, scanners and cellular phone handsets. Directly connecting such devices to each other rather than only to desktop (or laptop) computers is desirable.
However, the addition of host capability to an existing USB peripheral device, no matter how limited, is not a minor change. Additionally, there are no existing USB on-the-go (OTG) semiconductor devices that are “drop-in” (or close) replacements for existing USB peripheral silicon device families. Furthermore, the firmware requirements and architecture of a USB host is generally very different from that of a USB peripheral.
A typical USB OTG upgrade from legacy USB (i) requires substantial hardware re-design (i.e., USB peripheral silicon needs to be replaced with OTG dual role device silicon, resulting in new board design/layout), (ii) requires substantial firmware redesign (i.e., USB peripheral firmware is typically structured differently from host firmware, with different interrupt latency run-frequency required), (iii) has long time to market and substantial new product development investment that makes launching “pilot” products to test the market costly, (iv) lacks product range flexibility, (v) is difficult and expensive (i.e., vendors cannot provide both OTG and non-OTG devices on the same platform) and (vi) does not provide an upgrade path for the installed base or obsolete inventory of USB devices.
There is a general assumption among USB OTG suppliers that potential sales of OTG devices would be slow, and the transition from USB peripheral to OTG dual role device capability in most types of devices would take many years. In addition, the migration to OTG functionality in some otherwise relatively mature market segments will leave the owners and users of legacy USB peripherals with a potentially large but obsolete investment.
Therefore, product vendors may see a substantial drop-off in demand for legacy USB products after USB OTG products (with attendant enhanced functionality) are announced, but not yet available for purchase. The availability of an inexpensive accessory to add OTG functionality to legacy products would find a ready market with owners and users of older devices. Such an accessory could also be used by vendors to reduce the drop-off in demand during the introduction of new OTG products. Furthermore, obsolete stock could be upgraded to a saleable level of functionality.